A lamp such as, for example, a vehicular headlamp, takes a configuration in which a front cover as a light transmission body of a lamp housing that accommodates a lamp unit is formed of a light transmissive resin so as to transmit light emitted from the lamp unit through the front cover, thereby emitting the light toward a region in front of the vehicle. In the front cover, while an effective lighting portion—a region that transmits light therethrough—is molded only with a light transmissive resin, a non-effective lighting portion—a region that does not contribute to light distribution—is formed by laminating a colored light non-transmissive resin on a light transmissive resin so as to optically shield the inside of the lamp housing so that a part of the inside of the lamp cannot be visually recognized from the outside, thereby improving an external appearance. As disclosed in Japanese Patent Laid-Open Publication No. 2011-187299, such a front cover is frequently molded through a two-color molding method using a light transmissive resin and a light non-transmissive resin.
In the two-color molding method, a cavity is formed by a common mold and a primary mold, and a first resin portion is molded by introducing a first resin into the cavity. Subsequently, the primary mold is replaced with a secondary mold while the first resin portion is maintained in the common mold, and a second resin portion is molded by introducing a second resin into a cavity that is newly formed by the common mold and the secondary mold. Consequently, a two-color molded article in which the first resin portion and the second resin portion are integrated with each other is manufactured.